This invention relates to the field of production of powders containing generally spheroidal glass particles. One can use such powders as fillers for epoxy resins used in the manufacture of electronic components.
The electronics industry has used glass powders, and especially powders of fused silica (SiO.sub.2) in the manufacture of printed circuit boards and electronic components. An integrated circuit typically comes packed in a housing made of epoxy resin. Fused silica or other glasses form fillers for the epoxy resin. Up to 80% of a typical package which houses an integrated circuit may include fused silica.
Usually the fused silica or other glass powder contains particles having a diameter in the range of about 2-150 microns. The particles usually have rough edges, and have a non-spheroidal, several advantages result. First, if the particles have a spheroidal shape, the powder has a smaller total surface area, and one can pack the particles together more effectively. As a result, one requires less powder than one would need if the particles had rough edges.
Secondly, a powder composed of spheroidal particles "flows" more easily than a powder made of rough particles. Typically, one uses an injection molding device to shape a mixture of glass particles and epoxy resin. Making the particles spheroidal enables the mixture to pass through the molding device more easily. Since one can handle the mixture more readily, the manufacturing cost of the electronic circuit decreases.
Moreover, it turns out that the spheroidal shape of the particles contributes to the overall strength of the product, because of the tendency of spheroidal particles to become well-packed together.
While the prior art has recognized the desirability of producing spherical or spheroidal particles of glass, the methods of the prior art have not proved economical. For example, U.S. Pat. No. 4,961,770 shows a process for making spherical glass particles by heating the particles in a plasma reactor, at temperatures in the range of 5500.degree. C. to 17000.degree. C. While the patented process apparently works to produce the desired result, it operates at such high temperatures as to make the process uneconomical.
The present invention provides a method and apparatus which greatly reduces the cost of producing spheroidal glass particles. The apparatus of the present invention uses a slightly modified form of an oxygen-fuel burner, and operates at temperatures of only about 5000.degree. F. or less.